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As I review the spread of LP DHW heaters for my new home, I've run across some interesting literature and claims. Most interesting is study by Bradford-White that looked at the life cycle costs between 2 tank type heaters and 2 tankless units. For most people, a very efficient tank type unit will be best and least expensive over time even though 2 will be needed vs. one of the tankless units.

But I digress. The real question is: What if you buy a tankless with a remote temp control. When you take a shower or bath, you set the temp for exactly the temp water you need. When done, it can be reset a bit higher. This way, you are showering with the faucet set full hot and you are not heating any water past what is needed. The heater modulates to give you the perfect temp. No mixing with cold which is a waste of energy. Has anyone seen this or tried it? This would certainly change the cost savings equation and the aforementioned B-W study.

on demand gas HW heaters

I installed a Bosch 250SX (Natural Gas) and have been using it for over a month now.

This technology has a few minor querks, and even though I am only a homeowner, I will share with the HVAC because they probably need to be edumacated on this. And in oil to gas heat conversions, HVAC also do HW heaters as part of the package. The cost of installing these are significantly more than a traditional tank type and so are a hard sell.

First, obviously it takes a little longer to get hot water to the tap.

Second, the unit only turns on when the flow rate exceeds .8 GPM. This is a low threshold, but if you are a water miser, you will find that you may need to increase tap flow and waste more water than you like. Also, if you have a low flow shower head (2 GPM), and a well pump with a low pressure setting of 30 PSI, you may get a rude burst of cold water in the middle of your shower because you failed to exceed .8 GPM. Yikes!

Second, the digital temperature settings are impressive, but the unit will loose regulation at low and high flow rates. So somewhere between .8 GPM and X GPM, the unit cannot turn the flame down anymore and so you end up with very hot water. As a result, you may still need to mix when taking a shower or using the tap. And if you mix, you reduce hot water flow rate and risk shutting down. This of course depends on the flow rate of your shower head and delivery PSI.

I have compensated for this by increasing my well pump range to 35 / 52 . When taking a shower (2 GPM), I can use only hot water, with the unit set at 116 Deg and it will regulate. When using the tap, it is easy to mix so not a problem.

getting enough hot water or hot enough water has not been a problem for us.

About clothes washers, the new Kenmore's with water saving features are not the best fit with this type of water heater. These types have several short (30 sec) filling cycles which will result in uneven hot water deliverery because the heater is turning on and off repeatedly.

I also have a Bosch 250sx tankless

I agree with edumacated on his facts and opinions. I set the temp on exactly what I need at the shower, and leave it there. About 114-118 is what I need at the shower, and I rarely change it. I do not have the remote option, but it seemed interesting. I think Bosch does offer the remote, and other brands (Takagi etc.) do.

Mine has been in operation for about 4 months, and I have seen a noticable decline in costs so far, but with the variable weather factors it is hard to pinpoint the exact cause: sufice to say that my heating bill from Dec-March has gone from $16 per day down to $8-10 per day. I figure I am saving $50-80 a month, vs. the 75 gallon RO Smith tank HWH I had before.

That said, purchase/install cost was about $400 more than a comparible propane/ng tank heater, but the installation was much more involved, since I had to go from a standard vent to a dual intake/exhaust vent. I did the reroute of the gas supply, plumbing etc. myself, and it took me about 2 weeks to complete, doing a 1-2 hours a day (I am slow and methodical). However, i did do the install while the old one was still working (it was leaking), so the plumbing was a bit more involved. Also, I had to bore two holes in the brick wall, another pain I was not prepared for, but easier than expected. That cost about $100 in rental fees for a bore hammer/drill, so I figure my DIY install job at about $200 total.

The cost savings is two fold: the obvious is that you dont have heat loss from the tanks to the surrounding air and up the chimmny. The second is that normal house heat is also going up the chimmny, but I dont know how to quantify that. My savings also might be higher than most, as I have a large house (6000 sqr. feet), and I had a large tank at 75 gals. Although I feel I am saving more than $50 a month, I think $20-30 might be more realistic. My initial calcs at payback were 3 years vs. tank, but I might be ahead of schedule.

What about electric consumption? Difficult to isolate and quantify - but it seems to me it will have increased with the instantaneous heater, not to mention the added installation costs associated with power?

Re: I also have a Bosch 250sx tankless

Originally posted by dogturd .......Although I feel I am saving more than $50 a month, I think $20-30 might be more realistic. My initial calcs at payback were 3 years vs. tank, but I might be ahead of schedule.

Your calculations are legitimate IF the instanteous heater lasts. The ones I have run across haven't lasted, their service life is less than a conventional hot water heater. Time will tell I suppose.